The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Various types of temperature sensors can be used to measure a temperature change, by detecting material properties. Electrical temperature sensors, which detect a change in electrical material properties such as electrical resistance, are widely used. Examples of electrical temperature sensors include but are not limited to resistance temperature detectors (RTDs), thermistors, thermocouples, and semiconductor-junction temperature sensors.
Resistance values of resistive elements in RTDs and thermistors increase or decrease as a temperature increases. Semiconductor-junction devices (including diodes, metal-oxide-semiconductor field-effect transistors (MOSFET), and bipolar junction transistors (BJTs)) show a temperature dependent voltage-current behavior. For instance, a voltage across a p-n junction diode that is forward biased by a constant current, increases approximately linearly with decreasing temperature.
Such temperature dependent behavior of the electrical elements, can be used to generate a temperature dependent current i(T) that is proportional to absolute temperature (IPTAT) or inversely proportional to absolute temperature (ICTAT).
FIG. 1 illustrates a conventional digital temperature sensor device using a temperature dependent current i(T). The digital temperature sensor device 100 includes a temperature sensor 1-110, a current-to-voltage converter 1-120, and an analog-to-digital converter (ADC) 130.
The temperature sensor 1-110 generates the temperature dependent current i(T) that is proportional to absolute temperature (IPTAT) or inversely proportional to absolute temperature (ICTAT).
The current-to-voltage converter 1-120 converts the temperature dependent current i(T) generated by the temperature sensor 1-110, into a corresponding voltage V(T). Although a resistance value of a resistive element included in the current-to-voltage converter 1-120 may also vary according to a temperature change of the current-to-voltage converter 1-120, the temperature change is maintained within a sufficiently small range.
Thus, the resistance value typically remains at substantially the same value. Accordingly, the voltage V(T) generated by the current-to-voltage converter 1-120 shows substantially the same dependency on the temperature as the temperature dependent current i(T).
In analog temperature sensor devices, a temperature value (e.g. an analog value) corresponding to the current value i(T) or the voltage value V(T) is output. By contrast, in digital temperature sensors such as the digital temperature sensor device 100 of FIG. 1, the voltage V(T) is converted into an N-bit digital code (Tcode) using the ADC 130.